The U.S. Federal Communications Commission (FCC) has recently made E911 a mandatory requirement for wireless communications services such as cellular telephone, wideband (broadband) personal communications services (PCS), and geographic area specialized mobile radio (SMR). This ruling and upcoming service is called wireless E911. The FCC requires that by Oct. 1, 2001, public safety answering point (PSAP) attendants of wireless communications networks must be able to know a 911 caller's phone number for return calls and the location of the caller, so that the calls can be routed to an appropriate PSAP and related emergency assistance attendants.
The Global Positioning System (GPS) includes a network of satellites orbiting the earth and transmitting signals that can be detected by GPS receivers located on the ground. The GPS receivers, which decode and process the detected GPS satellite signals to determine precise location information of a user regardless of weather conditions, can be portable or mounted in ships, planes, cars, or in mobile wireless communication stations or mobile stations, such as radiotelephones, pagers, personal digital assistants (PDA), two-way radios, or similar wireless devices. In this way, GPS provides positioning and timing data that is used for a variety of applications, including determining the position of the mobile station to enable network operators to provide value-added services.
In assisted GPS mobile station positioning schemes, one or more ground based reference station or location server nodes, coupled to a cellular communications network, receive GPS satellite data and re-transmit the data in the form of assistance messages over the cellular air interface to mobile stations for use in position determination.
FIG. 1 is a schematic diagram of a typical cellular communication system. As illustrated in FIG. 1, a cellular communication system 100 includes a number of cells 102-114, each defining a radio coverage area established by a fixed site base station located within each cell. As illustrated in FIG. 1, cell 102 defines the radio coverage area established by a base station 116 coupled to an antenna 118 located in cell 102. Similarly, each of the remaining cells 104-114 define an associated coverage area established by corresponding base stations 120-130 coupled to corresponding antennas 132-142 located within each of cells 104-114.
A cellular communications network 144 coupled to a GPS reference receiver 146 receives data from a GPS network of satellites 148 through GPS reference receiver 146 and re-transmits the data in the form of assistance messages over an interface or fixed link 150 via other nodes to base stations 116 and 120-130. The assistance data is then transmitted over the air via antennas 118 and 132-142 in a point-to-point mode to a single wireless mobile station, or in a point-to-multipoint mode or broadcast mode to multiple wireless mobile stations along a cellular carrier signal 152. It is understood that while a single GPS reference receiver is shown in FIG. 1 for brevity, network 144 receives data from GPS network of satellites 148 through multiple GPS reference receivers or a wide area differential GPS reference receiver network.
As a wireless mobile station 154 travels with a user from position x to position y in cellular communication system 100, mobile station 154 continuously monitors the signal characteristics from base stations 116, 120-130 of cells 102-114 and, based on certain selection criteria, selects or is directed to a cell from which to receive and transmit signals, including the assistance data, with network 144. For example, while mobile station 154 is positioned in cell 112, if the signal characteristics from cell 112 are such that, based on the selection criteria, cell 112 is selected as the “best” coverage area, cell 112 is considered to be the “serving cell”, or cell from which mobile station 154 transmits and receives signals. Mobile station 154 continues to monitor the signal characteristics from cells 102-114, and, as illustrated in FIG. 1, as mobile station 154 subsequently moves along the marked path from position x to position y, mobile station 154 moves from the coverage area associated with cell 112 into the coverage area associated with other cells, such as cells 114 and 106 for example. Once the signal characteristics from another cell, cell 114 for example, are such that that cell is considered the best cell, mobile station 154 or network 144 reselects or determines that cell as the serving cell, until the signal characteristics from another cell, cell 106 for example, are such that that cell is considered the best cell, and mobile station 154 or network 144 reselects or determines that cell as the serving cell, and so on.
It is possible for each of base stations 116, 120-130 in cellular communication system 100 to operate in one of various differing modes, such as an analog mode, a time division multiple access (TDMA) mode, a code division multiple access (CDMA) mode, a general packet radio service (GPRS) mode, wideband CDMA (W-CDMA) mode, or universal mobile telecommunications service (UMTS) mode, for example. It is also possible that each cell contains more than one base'station or contains co-located base stations in which each one operates in its own mode. As a result, in order to operate in each of cells 102-114, mobile station 154 is typically a multi-mode device able to operate in multiple modes, including CDMA/Analog, TDMA/Analog, GPRS/GSM, UMTS/GSM, W-CDMA/GSM, W-CDMA/GPRS/GSM, and cdma2000/cdmaOne.
Since cells 102-114 operate in various different modes, mobile station 154 must also switch between modes as required during the cell reselection and “handover”. For example, if cell 112 operates in the CDMA mode, cell 114 operates in the analog mode, and cell 106 operates in the CDMA mode, mobile station 154 must switch from the CDMA mode to the analog mode when reselecting or transitioning from cell 112 to cell 114, and from the analog mode to the CDMA mode when reselecting or transitioning from cell 114 to cell 106, and so forth.
However, since the rate at which data can be transmitted when in an analog mode is much less than the rate at which data can be transmitted when in a CDMA mode or a TDMA mode, for example, transmission of the location assistance data becomes problematic when mobile station 154 selects or transits to an analog cell as a serving cell. Accordingly, a method and apparatus is needed for improving transmission, by avoiding transmission of assistance data or any type of data when a multi-mode device is in a slow data rate mode, for example analog mode.
Although the present invention is illustrated in these figures, the drawings and following description are not be interpreted as limiting the innovation. They are used to describe this invention for the purpose of fully understanding. In certain cases, well-known or conventional details are not included.